Apparatus and Methods for Estimating Time-State Physiological Parameters

ABSTRACT

A method of determining a value of a physiological parameter for a subject at a selected state includes obtaining, via a device located a distance from the subject, a value of the physiological parameter of the subject at a particular time-of-day, and applying a time-dependent relationship function to the obtained physiological parameter value via a processor to determine a value of the physiological parameter at the selected state.

RELATED APPLICATIONS

This application is a continuation application of pending U.S. patent application Ser. No. 15/219,770, filed Jul. 26, 2016, which is a continuation application of U.S. patent application Ser. No. 14/116,641, filed Nov. 8, 2013, now U.S. Pat. No. 9,427,191, which is a 35 U.S.C. §371 national stage application of PCT Application No. PCT/US2012/046446, filed Jul. 12, 2012, which claims the benefit of and priority to U.S. Provisional Patent Application No. 61/511,238 filed Jul. 25, 2011, the disclosures of which are incorporated herein by reference as if set forth in their entireties.

FIELD OF THE INVENTION

The present invention relates generally to monitoring apparatus and methods and, more particularly, to physiological monitoring apparatus and methods.

BACKGROUND OF THE INVENTION

Physiological parameters for living beings are typically a function of one or more of the following: the time-of-day, environmental conditions to which a being is exposed, activity level of a being, and various other physiological parameters. Many of these are related. For example, the average change in heart rate, body temperature, and heart rate variability (HRV) with the time-of-day are generally known based on human and animal studies of the circadian cycle.

SUMMARY

It should be appreciated that this Summary is provided to introduce a selection of concepts in a simplified form, the concepts being further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of this disclosure, nor is it intended to limit the scope of the invention.

According to some embodiments of the present invention, a method of determining a value of a physiological parameter for a subject at a selected state (e.g., state of peak metabolism, state of lowered metabolism, state of rest, etc.), includes obtaining, via a device attached to the subject, a value of the physiological parameter of the subject at a particular time-of-day, and applying a time-dependent relationship function to the obtained physiological parameter value via at least one processor to determine a value of the physiological parameter at the selected state. Exemplary physiological parameters include, but are not limited to, subject body temperature, subject heart rate, subject heart rate variability, subject blood gas levels, subject metabolic rate, subject respiration rate, subject blood analyte levels, subject blood pressure, subject pulse pressure, etc. In some embodiments of the present invention, the time-dependent relationship function is derived from a circadian rhythm for the subject. In some embodiments of the present invention, the time-dependent relationship function is a lookup table.

In some embodiments of the present invention, determining a value of the physiological parameter of the subject at a selected state may include obtaining the value of the physiological parameter at the same time-of-day for multiple days and determining an average value for the multiple obtained values. Applying the time-dependent relationship function to the obtained physiological parameter value may include applying the time-dependent relationship function to the average value.

In some embodiments of the present invention, determining a value of a physiological parameter for a subject at a selected state may further include determining if the subject is in a condition of heightened activity at the selected time-of-day by determining via the device if at least one obtained physiological parameter value is at a level associated with the heightened activity condition. The time-dependent relationship function is adjusted for the heightened activity condition of the subject prior to determining a value of the physiological parameter at the selected state.

In some embodiments of the present invention, prior to obtaining a value of the physiological parameter of the subject at a particular time-of-day, values of the physiological parameter of the subject are obtained at multiple times during at least one previous day. A personalized time-dependent relationship function between at least one obtained value of the physiological parameter and a value of the physiological parameter at a time when the subject is at the selected state is generated for the subject using the obtained values from the at least one previous day. Applying the time-dependent relationship function to the obtained physiological parameter value includes applying the personalized time-dependent relationship function to the obtained physiological parameter value via at least one processor to determine a value of the physiological parameter at the selected state.

In some embodiments of the present invention, the time-dependent relationship function is adjusted for calories consumed by the subject prior to determining a value of the physiological parameter at a time when the subject is at the selected state.

In some embodiments of the present invention, the time-dependent relationship function is adjusted for blood oxygen level of the subject prior to determining a value of the physiological parameter at a time when the subject is at the selected state.

In some embodiments of the present invention, the device includes at least one physiological sensor that is configured to detect and/or measure physiological information from the subject to which the device is attached.

In some embodiments of the present invention, the device includes at least one environmental sensor that detects and/or measures environmental condition information in a vicinity of the subject. Determining a value of a physiological parameter for a subject at a selected state, according to some embodiments of the present invention, further comprises obtaining, via the device, a value of an environmental parameter in a vicinity of the subject at the particular time-of-day. Applying the time-dependent relationship function to the obtained physiological parameter value comprises applying the time-dependent relationship function and an environmental-dependent relationship function to the obtained physiological parameter value via the at least one processor to determine a value of the physiological parameter at a time when the subject is at the selected state.

Devices according to embodiments of the present invention may be configured to be attached to various portions of the body of a subject including, but not limited to, ear, arm, wrist, leg, hand, foot, finger, toe, chest, head, hair, nose, waist, trunk, shoulder, and neck. Devices according to embodiments of the present invention may also be configured to be embedded within clothing, foot apparel, and other wearable objects, without limitation. Additionally, devices according to embodiments of the present invention may be worn outside the body so as to be noninvasive, may be worn inside the body so as to be invasive, or may be worn subdermally so as to be mildly invasive.

According to other embodiments of the present invention, a method of determining a value of a physiological parameter (e.g., subject body temperature, subject heart rate, subject heart rate variability, subject blood gas levels, subject metabolic rate, subject respiration rate, subject blood analyte levels, subject blood pressure, and subject pulse pressure, etc.) for a subject at rest comprises obtaining, via a device attached to the subject, a value of the physiological parameter of the subject at a particular time-of-day, and applying a time-dependent relationship function to the obtained physiological parameter value via at least one processor to determine a value of the physiological parameter at a time when the subject is at rest.

In some embodiments of the present invention, determining a value of the physiological parameter of the subject at rest comprises obtaining the value of the physiological parameter at the same time-of-day for multiple days and determining an average value for the multiple obtained values. Applying the time-dependent relationship function to the obtained physiological parameter value may include applying the time-dependent relationship function to the average value.

In some embodiments of the present invention, determining a value of a physiological parameter for a subject at rest may further include determining if the subject is in a condition of heightened activity at the time-of-day by determining via the device if at least one obtained physiological parameter value is at a level associated with heightened activity. The time-dependent relationship function is adjusted for the heightened activity condition of the subject prior to determining a value of the physiological parameter at a time when the subject is at rest.

In some embodiments of the present invention, prior to obtaining a value of the physiological parameter of the subject at the time-of-day, values of the physiological parameter of the subject are obtained at multiple times during at least one previous day. A personalized time-dependent relationship function between at least one obtained value of the physiological parameter and a value of the physiological parameter at a time when the subject is at rest is generated for the subject using the obtained values from the at least one previous day. Applying the time-dependent relationship function to the obtained physiological parameter value includes applying the personalized time-dependent relationship function to the obtained physiological parameter value via the processor to determine a value of the physiological parameter at a time when the subject is at rest.

In some embodiments of the present invention, the time-dependent relationship function is adjusted for calories consumed by the subject prior to determining a value of the physiological parameter at a time when the subject is at rest.

In some embodiments of the present invention, the time-dependent relationship function is adjusted for blood oxygen level of the subject prior to determining a value of the physiological parameter at a time when the subject is at rest.

In some embodiments of the present invention, the device includes at least one environmental sensor that detects and/or measures environmental condition information in a vicinity of the subject. Determining a value of a physiological parameter for a subject at rest, according to some embodiments of the present invention, further comprises obtaining, via the device, a value of an environmental parameter in a vicinity of the subject at a particular time-of-day. Applying the time-dependent relationship function to the obtained physiological parameter value comprises applying the time-dependent relationship function and an environmental-dependent relationship function to the obtained physiological parameter value via at least one processor to determine a value of the physiological parameter at a time when the subject is at rest.

According to other embodiments of the present invention, a method of determining a value of a physiological parameter for a subject at a selected state (e.g., state of peak metabolism, state of lowered metabolism, state of rest, etc.) includes obtaining, via a device attached to the subject, a value of the physiological parameter (e.g., subject body temperature, subject heart rate, subject heart rate variability, subject blood gas levels, subject metabolic rate, subject respiration rate, subject blood analyte levels, subject blood pressure, and subject pulse pressure, etc.) of the subject at a selected time-of-day; obtaining, via the device, a value of an environmental parameter in a vicinity of the subject at the selected time-of-day via the environmental sensor; determining if the subject is in a condition of heightened activity at the selected time-of-day by determining via the device if at least one obtained physiological parameter value is at a level associated with heightened activity; and applying a time-dependent relationship function and an environmental-dependent relationship function to the obtained physiological parameter value via a processor to determine a value of the physiological parameter at the selected state, wherein the time-dependent relationship function is adjusted for the heightened activity condition of the subject prior to determining a value of the physiological parameter at the selected state.

In some embodiments of the present invention, obtaining a value of the physiological parameter of the subject at a particular time-of-day includes obtaining the value at the same time-of-day for multiple days and determining an average value for the multiple obtained values. Applying the time-dependent relationship function and the environmental-dependent relationship function to the obtained physiological parameter value includes applying the time-dependent relationship function and the environmental-dependent relationship function to the average value.

In some embodiments of the present invention, prior to obtaining a value of the physiological parameter of the subject at a particular time-of-day, values of the physiological parameter of the subject are obtained at multiple times during at least one previous day, and a personalized time-dependent relationship function between at least one obtained value of the physiological parameter and a value of the physiological parameter at the selected state is generated for the subject using the obtained values from the at least one previous day. Applying the time-dependent relationship function and the environmental-dependent relationship function to the obtained physiological parameter value includes applying the personalized time-dependent relationship function and the environmental-dependent relationship function to the obtained physiological parameter value via at least one processor to determine a value of the physiological parameter at the selected state.

In some embodiments of the present invention, the time-dependent relationship function is adjusted for calories consumed by the subject prior to determining a value of the physiological parameter at the selected state.

In some embodiments of the present invention, the time-dependent relationship function is adjusted for blood oxygen level of the subject prior to determining a value of the physiological parameter at the selected state.

According to other embodiments of the present invention, an apparatus includes a housing configured to be attached to a subject and at least one physiological sensor attached to the housing, wherein the at least one physiological sensor detects and/or measures physiological information from the subject. At least one processor may be attached to the housing or may be located remotely from the housing. The at least one processor is in communication with the at least one physiological sensor and is configured to obtain from the at least one physiological sensor a value of a physiological parameter of the subject at a particular time-of-day, and to apply a time-dependent relationship function to the obtained physiological parameter value to determine a value of the physiological parameter at a selected state.

In some embodiments of the present invention, the at least one processor is configured to obtain from the at least one physiological sensor the value of the physiological parameter at the same time-of-day for multiple days, determine an average value for the multiple obtained values, and apply the time-dependent relationship function to the average value.

In some embodiments of the present invention, the at least one processor is configured to determine if the subject is in a condition of heightened activity at the time-of-day by determining if at least one obtained physiological parameter value is at a level associated with heightened activity, and adjust the time-dependent relationship function for the heightened activity condition of the subject prior to determining a value of the physiological parameter at the selected state.

In some embodiments of the present invention, the at least one processor is configured to obtain values of the physiological parameter of the subject at multiple times during at least one previous day, generate a personalized time-dependent relationship function between at least one obtained value of the physiological parameter and a value of the physiological parameter at the selected state using the obtained values from the at least one previous day, and apply the personalized time-dependent relationship function to the obtained physiological parameter value to determine a value of the physiological parameter at the selected state.

In some embodiments of the present invention, the apparatus includes an environmental sensor that detects and/or measures environmental condition information in a vicinity of the subject. The at least one processor is configured to obtain a value of an environmental parameter in a vicinity of the subject at a particular time-of-day from the environmental sensor, and to apply the time-dependent relationship function and an environmental-dependent relationship function to the obtained physiological parameter value to determine a value of the physiological parameter at the selected state.

In some embodiments of the present invention, the at least one processor is configured to adjust the time-dependent relationship function for calories consumed by the subject prior to determining a value of the physiological parameter at the selected state.

In some embodiments of the present invention, the at least one processor is configured to adjust the time-dependent relationship function for blood oxygen level of the subject prior to determining a value of the physiological parameter at the selected state.

In some embodiments of the present invention, the housing is configured to be attached to an ear of the subject. In other embodiments, the housing is configured to be attached to one or more of the following portions of a body of a subject: arm, wrist, leg, hand, foot, finger, toe, chest, head, hair, nose, waist, trunk, shoulder, and neck. In other embodiments, the housing is configured to be embedded within clothing, foot apparel, and other wearable objects, without limitation.

Conventional methods and apparatus for studying the circadian cycle heretofore have not estimated resting state (or other) parameters of a being based on the current state of the being. There have been at least two major limitations preventing such an invention: 1) there has been no effort to estimate resting parameters based on what's already known about the relationships between resting state and current state and 2) there have been no apparatuses or methods for accurately and reliably measuring dynamically changing relationships between current and resting state parameters in everyday life activities.

It is noted that aspects of the invention described with respect to one embodiment may be incorporated in a different embodiment although not specifically described relative thereto. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination. Applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to be able to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner. These and other objects and/or aspects of the present invention are explained in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which form a part of the specification, illustrate various embodiments of the present invention. The drawings and description together serve to fully explain embodiments of the present invention.

FIG. 1 is a block diagram of methods and apparatus for estimating physiological parameters of a being at a selected state, according to some embodiments of the present invention.

FIG. 2 is an exemplary plot of how tympanic or core body temperature may change with time-of-day for an average person.

FIG. 3 is an exemplary plot of how heart rate may change with time-of-day for an average person, wherein curve C1 represents a normal cycle and wherein curve C2 represents an elevated cycle.

FIG. 4 is an exemplary plot of how heart rate variability (HRV) may change with time-of-day for an average person.

FIG. 5 is an exemplary plot of how heart rate of a person may change with the person's activity level.

FIG. 6 is a flow chart for an algorithm for estimating resting parameters, according to some embodiments of the present invention.

FIG. 7 is a plot of average body temperature vs. time calculated using a polynomial equation for body vs. time-of-day, according to some embodiments of the present invention.

FIG. 8 is a plot of heart rate vs. time for an average person, wherein curve (A) represents heart rate vs. time before a lifestyle change, wherein curve (B) represents heart rate vs. time after a lifestyle change, and wherein curve (A) and (B) are generated via respective polynomial equations according to some embodiments of the present invention.

FIG. 9 illustrates a functional relationship between an estimated parameter and multiple time-dependent inputs, according to some embodiments of the present invention.

FIG. 10 is an exemplary lookup table for estimating resting body temperature, according to some embodiments of the present invention.

FIG. 11 is a block diagram that illustrates details of an exemplary processor and memory that may be used in accordance with embodiments of the present invention.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter with reference to the accompanying figures, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Like numbers refer to like elements throughout. In the figures, certain layers, components or features may be exaggerated for clarity, and broken lines illustrate optional features or operations unless specified otherwise. In addition, the sequence of operations (or steps) is not limited to the order presented in the figures and/or claims unless specifically indicated otherwise. Features described with respect to one figure or embodiment can be associated with another embodiment or figure although not specifically described or shown as such.

It will be understood that when a feature or element is referred to as being “on” another feature or element, it can be directly on the other feature or element or intervening features and/or elements may also be present. In contrast, when a feature or element is referred to as being “directly on” another feature or element, there are no intervening features or elements present. It will also be understood that, when a feature or element is referred to as being “connected”, “attached” or “coupled” to another feature or element, it can be directly connected, attached or coupled to the other feature or element or intervening features or elements may be present. In contrast, when a feature or element is referred to as being “directly connected”, “directly attached” or “directly coupled” to another feature or element, there are no intervening features or elements present. Although described or shown with respect to one embodiment, the features and elements so described or shown can apply to other embodiments. It will also be appreciated by those of skill in the art that references to a structure or feature that is disposed “adjacent” another feature may have portions that overlap or underlie the adjacent feature.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Spatially relative terms, such as “under”, “below”, “lower”, “over”, “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if a device in the figures is inverted, elements described as “under” or “beneath” other elements or features would then be oriented “over” the other elements or features. Thus, the exemplary term “under” can encompass both an orientation of over and under. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. Similarly, the terms “upwardly”, “downwardly”, “vertical”, “horizontal” and the like are used herein for the purpose of explanation only unless specifically indicated otherwise.

It will be understood that although the terms first and second are used herein to describe various features/elements, these features/elements should not be limited by these terms. These terms are only used to distinguish one feature/element from another feature/element. Thus, a first feature/element discussed below could be termed a second feature/element, and similarly, a second feature/element discussed below could be termed a first feature/element without departing from the teachings of the present invention.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Well-known functions or constructions may not be described in detail for brevity and/or clarity.

The term “housing”, as used herein, may refer to a physical structure for supporting and/or unifying one or more physical elements of the invention. For example, the housing of a wearable wrist sensor apparatus or headset sensor apparatus may comprise a structure to support the electronics, optics, and/or mechanical elements of the sensor. Two specific, non-limiting examples of a housing may be a “clamshell” of an earbud or one or more PCB boards for the sensor electronics. The structure may be composed of plastic, metal, polymer, ceramic, glass, composite material, or virtually any solid stable enough to support the physical elements of the apparatus.

The term “selected state”, as used herein, includes, but is not limited to, state of peak metabolism, state of lowered metabolism, state of rest, a state of one's psychology or mental functioning or the body's physiology or physiological functioning. Any example of mental functioning may include psychosocial stress, mental stress, mental acuity, brain activity, conscious state, state or phase of sleep, or the like. An example of physiological functioning may include the functioning of one or more organs individually or in unison. In addition, a selected state may refer to a particular time of day where a particular or noteworthy mental or physiological event may take place.

The term “heightened activity condition”, as used herein, includes, but is not limited to, elevated heart rate, elevated or lowered vital signs status, such as heart status (heart rate, ECG waveform intervals, cardiac output, cardiac stress or load, or the like), lung status (breathing rate, breathing volume, lung stress or load, or the like), blood pressure, blood oxygen level, heart rate variability, galvanic skin response, heat flux from the body, core body temperature, skin temperature, sympathetic or parasympathetic response, or the like.

The term “blood analyte” may refer to blood constituents, such as blood gases (blood oxygen, blood CO₂, blood hemoglobin, and the like), blood glucose, blood cholesterol, blood lactic acid, blood bilirubin, dissolved species in the blood, and the like.

The term “headset” includes any type of device or earpiece that may be attached to or near the ear (or ears) of a user and may have various configurations, without limitation. Headsets as described herein may include mono headsets (one earbud) and stereo headsets (two earbuds), earbuds, hearing aids, ear jewelry, face masks, headbands, and the like.

The term “real-time” is used to describe a process of sensing, processing, or transmitting information in a time frame which is equal to or shorter than the minimum timescale at which the information is needed. For example, the real-time monitoring of pulse rate may result in a single average pulse-rate measurement every minute, averaged over 30 seconds, because an instantaneous pulse rate is often useless to the end user. Typically, averaged physiological and environmental information is more relevant than instantaneous changes. Thus, in the context of embodiments of the present invention, signals may sometimes be processed over several seconds, or even minutes, in order to generate a “real-time” response.

The term “monitoring” refers to the act of measuring, quantifying, qualifying, estimating, sensing, calculating, interpolating, extrapolating, inferring, deducing, or any combination of these actions. More generally, “monitoring” refers to a way of getting information via one or more sensing elements. For example, “blood health monitoring” includes monitoring blood gas levels, blood hydration, and metabolite/electrolyte levels.

The term “physiological” refers to matter or energy of or from the body of a creature/subject (e.g., humans, animals, etc.). In embodiments of the present invention, the term “physiological” is intended to be used broadly, covering both physical and psychological matter and energy of or from the body of a creature. However, in some cases, the term “psychological” is called-out separately to emphasize aspects of physiology that are more closely tied to conscious or subconscious brain activity rather than the activity of other organs, tissues, or cells. Embodiments of the present invention are not limited to use by only humans.

The term “body” refers to the body of a subject (human or animal) who may wear a headset incorporating embodiments of the present invention.

The terms “being”, “creature”, “subject”, and “organism”, as used herein, are interchangeable and include, but are not limited to, humans and animals.

The terms “circadian rhythm” and “circadian cycle”, as used herein, are interchangeable and refer to an endogenously driven, roughly 24-hour cycle in biochemical, physiological, or behavioral processes.

The term “processor” refers to a device that takes one form of information and converts this information into another form, typically having more usefulness than the original form. For example, in this invention, a signal processor may collect raw physiological and environmental data from various sensors and process this data into a meaningful assessment, such as pulse rate, blood pressure, or air quality. A variety of microprocessors or other processors may be used herein. The terms “signal processor”, “processor”, “controller”, and “microcontroller”, as used herein, are interchangeable.

Embodiments of the present invention provide methods and apparatus for estimating time-state physiological parameters/assessments, such as resting parameters, of a subject by factoring functional relationships between the time-dependent parameters and other measured factors. For example, current state parameters (such as vital signs, environmental exposures, time-of-day, and the like) are measured and a physiological model is applied to generate an estimation of resting state parameters (or other particular states) of the subject. These relationships can be static relationships based on models that apply knowledge of how a current state of the subject relates to a resting state of the subject. These relationships can also be dynamic relationships based on personalized monitoring of a subject throughout various life activities.

Average body temperature, heart rate, heart rate variability for a subject, as well as many other vital parameters, change throughout the day on a regular schedule dependent on the time-of-day, consistent with normal circadian rhythms. Additionally, average values of vital signs will change throughout the day based on changes in a subject's physical activity or metabolic rate. As shown in FIGS. 2 and 7, average body temperature for a human subject may change by ˜2° F. from early morning to mid-day. In FIG. 2, body temperature is plotted on the y-axis and time in hours is plotted on the x-axis. Curve 100 in FIG. 2 is a plot of average core body temperature vs. time for an average human over an average day. In FIG. 7, body temperature is plotted on the y-axis and time in hours is plotted on the x-axis. Polynomial equation 104 is used to calculate the plot 102.

Similarly, as shown in FIG. 3, average heart rate for a human subject may change by ˜15 BPM (beats per minute) during that same period. FIG. 3 illustrates how heart rate may change with time-of-day for an average person, wherein curve C1 represents a normal cycle and wherein curve C2 represents an elevated cycle. In FIG. 3, heart rate is plotted on the y-axis and time in hours is plotted on the x-axis. Thus, if average body temperature and average heart rate are being monitored throughout the day, estimating resting body temperature and resting heart rate for a subject may be derived by applying the respective relationships to the existing measured state.

For example, if the current state at mid-day shows a body temperature of 99.6° F. and heart rate of 80 BPM, the resting state values may be estimated as 97.6° F. and 65 BPM, by subtracting 2° F. from body temperature and 15 BPM from heart rate, respectively. Percent (%) change relationships for estimating resting state, as opposed to absolute value changes, may also be used to estimate resting state. For example, the change from current state to resting state in the aforementioned case is ˜2% and 18% for body temperature and resting heart rate, respectively. Thus, a lookup table (e.g., table 110, FIG. 10) may be generated with time-of-day in one column, measured value in a second column, and the associated percent multiplier in a third column, where the percent multiplier is the ratio between resting value and measured value. The estimation for resting value can then be generated by multiplying this time-of-day-dependent ratio by the measured vital parameter at the given time-of-day of the measurement.

A specific example for the case of body temperature is presented in FIG. 10, using the same relationships and data of FIG. 2, where a measurement of body temperature has been made at 6 PM, with a multiplier of ˜0.981, yielding a resting body temp estimate of 97.6° F. A complimentary lookup table may replace the % multiplier column with a ±add/subtract column, where the ±number is the amount to add or subtract from the measured value to generate an estimate of the resting value.

It should also be noted that a formula, rather than a lookup table, may also be used to relate resting estimates to measured estimates, depending on the time-of-day. For example, a polynomial formula representing the table of FIG. 10 may be: Estimated Resting Value=(Measured Value)*(−0.29x⁴+0.79x³−0.63x²+0.13x+1.0), where x=time in hours, starting at x=0 for 7 AM. It is apparent from this formula that at 7 AM (x=0), the Estimated Resting Value=Measured Value, which is expected in the aforementioned formalism.

FIG. 7 shows an exemplary plot 102 of average human body temperature during a day, along with an approximate functional relationship for average body temperature vs. time. In the illustrated embodiment, the functional relationship is a polynomial equation 104 of order n=4. The a₀ term is 97.6° F., representing the resting body temperature, or BT_(resting)=97.6° F. If a person's resting body temperature (BT_(resting)) had started higher or lower than 97.6° F., the polynomial equation may still hold, with the only substantial difference being the a₀ term for BT_(resting). Thus, an equation for estimating BT_(resting) VS. BT_(measured) may be derived by rearranging terms such that a₀=BT_(resting)=BT_(measured)−[9E−05(t⁴)−0.0033(t³)+0.0161(t²)+0.2868(t)]. More generally, a₀=BT_(resting)=BT_(measured)−[a_(n)(t^(n))+a_(n-1)(t^(n-1))+a_(n-2)(t^(n-2))+ . . . a₁(t)], where “n” is the order of the polynomial equation and where t=0 represents the value of BT at the resting state. The second term in the brackets may be related to body temperature changes due to circadian rhythms, such that BT_(resting)=BT_(measured)−Δ BT_(circadian). This same general relationship may be applied towards heart rate (HR) as shown in FIG. 3 and heart rate variability in FIG. 4. In FIG. 4, heart rate variability is plotted on the y-axis and time in hours is plotted on the x-axis. The units along the y-axis are milliseconds-squared. Plot 120 illustrates how heart rate variability (HRV) may change with time-of-day for an average person. For example, HR_(resting)=HR_(measured)−Δ HR_(circadian) and HRV_(resting)=HRV_(measured)−Δ HRV_(circadian). This formalism may be applied towards blood oxygen (SPO₂), respiration rate (RR), blood pressure (BP), pulse pressure (PP), and other vital parameters (VP), that may change regularly throughout the day according to VP_(resting)=VP_(measured)−Δ VP_(circadian).

In some embodiments of the present invention, the general relationships illustrated in FIGS. 2, 3, and 7 may not enable a prediction of resting state (or other selected state) as accurately as desired. For example, a person engaging in heightened activity or personal variations may cause substantial departures from the general relationships. Fortunately, these differences may effectively average out if vital signs measurements are made over a period of time. For example, if a vital sign of interest is measured over several days at the same time-of-day, during different activity levels, the average value of the vital sign may be largely divorced of convolutions caused by heightened or acute activity. This average value of VP_(measured) may then be used to estimate VP_(resting). However, it may be difficult to measure the vital parameter at the same time-of-day for multiple days, and a one-time measurement of a vital parameter taken during or following high activity may not be sufficient to support an accurate estimate of the resting value, using the general relationships alone.

To correct for conditions of high activity, a general relationship between changes in activity and changes in vital parameters may be used to correct an estimate of resting parameters, according to some embodiments of the present invention. For example, during activity, the heart rate of a subject may increase in a predictable fashion, as shown in FIG. 5. In FIG. 5, heart rate is plotted on the left y-axis, activity is plotted on the right y-axis, and time in hours is plotted on the x-axis. Curve A in FIG. 5 illustrates heart rate and activity for a person at a first state, and curve B in FIG. 5 illustrates heart rate and activity for the person at a heightened activity state.

Generally, as illustrated in FIG. 5, heart rate will increase with activity, and the rate of increase with activity may be proportional to the physical fitness or aerobic capacity (VO₂max) of the subject. Thus, if the relationship between heart rate and activity is known for a subject, then the differential increase in heart rate due to elevated activity, for a particular time-of-day, may be subtracted from the current heart rate measurement. Namely, the estimated resting heart rate can be defined as HR_(resting)=HR_(measured)−Δ HR_(circadian)−Δ HR_(activity), where Δ HR_(activity) is the change in heart rate with activity (either positive/negative for increases/decreases in heart rate with activity). For other vital parameters, the term Δ VP_(activity) may be used instead.

Personal differences between individuals may cause deviations from the general, “universal” relationships previously described. For example, subjects having a higher metabolic rate change throughout a given day may have a larger total value or percent change in vital parameters between early morning and midday. Improving the accuracy of estimating resting parameters can be achieved by measuring vital parameters throughout the day, generating average time-dependent relationships based on these measured parameters, and deriving a personalized time-dependent relationship between measured and resting parameters. Once a personalized, functional, time-dependent relationship is generated between measured (current state) vital parameters and resting state vital parameters, this model may be used to estimate resting state parameters by inputting current state measurements into the model. For current state measurements taken at high activity, stored relationships between a subject's vital parameters and activity can be employed to subtract the change in vital parameter values with activity (Δ VP_(activity)) as with the heart rate example described above.

Environmental exposures (i.e., environmental conditions to which a subject is exposed) may also affect the time-dependent relationship between measured and resting parameters. For example, sunlight exposure may elevate metabolism, resulting in an increase in heart rate, breathing, rate, other vital parameters, or the like. In such case, it may be insufficient to estimate resting parameters by simply measuring current resting parameters and inputting current parameters into the functional model. Rather, it may be more accurate to estimate resting vital parameters according to VP_(resting)=VP_(measured)−Δ VP_(circadian)−Δ VP_(environmental exposure) where Δ VP_(environmental exposure) is the change (positive or negative) in the vital parameter value due to environmental exposure (e.g., sunlight exposure, etc.). A change in vital parameters may be caused by many different forms of environmental exposures such as, but not limited to, loud noises, strong wind, extreme temperatures, short wavelength light (e.g., light at wavelengths <470 nm), airborne pollution, mechanical stress, and the like.

It should be noted that multiple parameters may simultaneously affect the relationship between resting values and measured values. For example, if physical activity and environmental exposure both have an impact on instantaneous vital parameters, then a more general relationship for resting vital parameters may be: VP_(resting)=VP_(measured)−Δ VP_(circadian)−Δ VP_(activity)−Δ VP_(environmental exposure). Additional relationships, such as changes in a vital parameter with food intake (calories consumed), blood oxygen (SPO₂), and the like may also be incorporated. These additional relationships can be accommodated by Δ VPn, where the integer “n” represents an additional factor which may affect VP_(measured).

The aforementioned models for estimating resting parameters have been presented as “static” models. A static model, once implemented or derived, stays fixed with time. However, models for determining a value of a physiological parameter for a subject at a selected state (e.g., at rest, etc.), according to some embodiments of the present invention, may also be dynamic, changing with time based on updated information about a particular person or group of people. For example, a person undergoing cardiac therapy, a new diet, drug therapy, or other lifestyle change may see an acute or chronic change in metabolism over time. In such case, static models may be insufficient for estimating resting parameters from current state measured parameters. Rather, it may be more accurate to measure vital parameters over a period of time and update the model based on updated relationships between resting and current state parameters.

FIG. 8 shows a specific example of a dynamic model for determining a value of a physiological parameter for a subject at a selected state (e.g., at rest, etc.) according to some embodiments of the present invention. FIG. 8 is a graph of heart rate vs. time-of-day for a twenty-four hour (24 hr) period. Curves A and B in FIG. 8 show the circadian change in average heart rate profile of an average person before and after a lifestyle change. Polynomial representations of these plots are also shown, with a polynomial order of n=5. Polynomial equation 130 is used to generate curve A in FIG. 8 and polynomial equation 140 is used to generate curve B in FIG. 8.

As illustrated in FIG. 8, after the lifestyle change, the average heart rate changes more dramatically as the time-of-day changes, as exemplified by the 2× increase in the 5th-power coefficient in the “B” curve when compared with the “A” curve. The resting heart rate for each case is the a₀ terms of each, 60 and 45 BPM for curves A and B, respectively. Because the change in each model (for curves A and B) is not merely a scalar addition or subtraction, accurately estimating resting heart rate may require measuring average heart rate throughout the day, over the course of several days, modeling a relationship between resting and current state parameters, and then inputting current state parameters into the model. In one embodiment of the present invention, the model may be a polynomial equation fit to the measured data, as shown in FIG. 8. However, other models may be employed to improve accuracy or model simplicity, according to embodiments of the present invention.

FIG. 1 is a block diagram of methods and apparatus for generating estimated physiological parameters of a subject at a selected state based on current state measurements, according to some embodiments of the present invention. Time-correlated physiological metrics (Block 10) and/or time-correlated environmental metrics (Block 20) are collected and are input into a physiological model (static, dynamic, or a combination of both) (Block 30), and the desired parameters (such as resting state parameters) are estimated (Block 40) based on the metrics and physiological model. The estimated parameters are then reported in an organized fashion (Block 50).

An algorithm for estimating a resting parameter according to embodiments of the present invention is presented in the flow chart of FIG. 6. The algorithm includes measuring time-correlated heart rate (HR), respiration rate (RR), activity levels, etc., at a particular time of day (Block 150). A physical model is applied to estimate a parameter value that accounts for changes in the time-correlated parameter with activity, environmental exposure, and/or daily cycle (Block 152). A resting assessment is then generated (Block 154).

FIG. 11 illustrates an exemplary processor 200 and memory 202 that may be used in a wearable device and/or a device remote from a subject to carry out various embodiments of the present invention. The processor 200 communicates with the memory 202 via an address/data bus 204. The processor 200 may be, for example, a commercially available or custom microprocessor or similar data processing device. The memory 202 is representative of the overall hierarchy of memory devices containing the software and data used to perform the various operations described herein. The memory 202 may include, but is not limited to, the following types of devices: cache, ROM, PROM, EPROM, EEPROM, flash, SRAM, and DRAM.

As shown in FIG. 11, the memory 202 may hold various categories of software and data: an operating system 206, a physiological data collection module 208, an environmental data collection module 210, and a time-dependent relationship function module 212. The operating system 206 controls operations of the physiological and environmental sensors.

It should be noted that estimating a physiological metric at a selected time state need not necessarily require a direct measurement of current time. For example, if the relationship between at least one physiological parameter and time is already known, or if that relationship is developed by recording data for a subject wearing a physiological sensor over time as shown in FIG. 11, then the current time may be inferred through this relationship and factored into an estimate for a second physiological metric at a selected time state. For example, if the relationship between the subject's core body temperature over time is known (as shown in FIG. 2), then a subject's HRV may be estimated for a selected time-state by estimating the current time based on the measured core body temperature at a current state. In such case, the current time need not be measured. However, in such case, because the current time is inferred and not directly noted or measured, it may be further beneficial to measure the subject's activity and have this factored into the relationship function 212 (as discussed for FIG. 5) so as to prevent activity-based artifacts from causing inaccurate estimates of a second physiological metric at a selected state.

The physiological data collection module 208 comprises logic for obtaining from a physiological sensor a value of a physiological parameter of a subject at a particular time-of-day. The physiological data collection module 208 may also comprise logic for obtaining from a physiological sensor the value of a physiological parameter at the same time-of-day for multiple days, and logic for determining an average value for the multiple obtained values. The physiological data collection module 208 may also comprise logic for obtaining values of a physiological parameter of a subject at multiple times during at least one previous day.

The environmental data collection module 210 comprises logic for obtaining from an environmental sensor a value of an environmental parameter in a vicinity of a subject at a particular time-of-day.

The time-dependent relationship function module 212 comprises logic for applying a time-dependent relationship function to an obtained physiological parameter value to determine a value of the physiological parameter at a selected state, and logic for applying the time-dependent relationship function and an environmental-dependent relationship function to an obtained physiological parameter value (and average value) to determine a value of the physiological parameter at the selected state. In addition, the time-dependent relationship function module 212 may comprise logic for determining if a subject is in a condition of heightened activity at a selected time-of-day by determining if at least one obtained physiological parameter value is at a level associated with heightened activity, and may comprise logic for adjusting the time-dependent relationship function for the heightened activity condition of the subject prior to determining a value of the physiological parameter at the selected state. The time-dependent relationship function module 212 may comprise logic for generating a personalized time-dependent relationship function between a measured value of a physiological value and a value of the physiological parameter at a selected state using obtained values from at least one previous day, and may comprise logic for applying the personalized time-dependent relationship function to a obtained physiological parameter value to determine a value of the physiological parameter at the selected state.

The time-dependent relationship function module 212 may also comprise logic for adjusting a time-dependent relationship function for calories consumed by a subject prior to determining a value of the physiological parameter at a selected state. The time-dependent relationship function module 212 may also comprise logic for adjusting a time-dependent relationship function for blood oxygen level of a subject prior to determining a value of the physiological parameter at a selected state.

According to some embodiments of the present invention, collecting measured time-dependent metrics may be manual or automatic. Records can be taken over time, recorded, and processed into time-dependent relationships by skilled professionals or personal recording. However, it may be easier to record this data with one or more wearable devices having multiple wearable sensors. For example, wired and wireless vital parameter modules may be located along several parts of the body, or integrated into a single device worn at a single place along the body. These wearable devices may measure vital parameters throughout the day and, with microprocessors or other processing devices, generate estimations for resting parameters. Memory devices, such as memory chips, data storage devices, and the like, may be used to store and update physiological models according to embodiments of the present invention, and at least one processor may be used to estimate parameters based on the metrics and model. At least one processor may also be used to organize the data into a string of outputs for each measured parameter. There is great flexibility in the electronics that may be used to implement embodiments of the present invention. Individual electronic components or chips may be used and integrated within circuit board, or the electronics may integrate memory storage, data processing, and data translation within a single chip, or other combinations or electronics configurations may be used.

Some types of wearable devices may be more suited for sensor integration than other devices. For example, an ear-worn device may be especially suited for measuring blood flow, heart rate, breathing rate, EEG, and body temperature, due in part to the location of the ear with respect to physiological structures such as the carotid artery, capillaries, ear blood vessels, the brain, and the tympanic membrane. However many other form-factors for a single wearable device may be employed. For example, strong blood flow and heat generation in the limbs, digits, and torso enable integrated sensor locations in the arms, wrist, legs, hands, feet, fingers, toes, chest, head, hair, nose, waist, trunk, shoulder, neck, and other locations. Furthermore, physiological and environmental sensors may be embedded in clothing or other wearable devices, such as headsets, earbuds, wrist watches, adhesive patches, rings, bracelets, necklaces, footwear, socks, shirts, pants, underwear, earrings and other body piercings, hats, glasses, and the like.

The ear is an ideal location for wearable health and environmental monitors. The ear is a relatively immobile platform that does not obstruct a person's movement or vision. Headsets located at an ear have, for example, access to the inner-ear canal and tympanic membrane (for measuring core body temperature), muscle tissue (for monitoring muscle tension), the pinna and earlobe (for monitoring blood gas levels), the region behind the ear (for measuring skin temperature and galvanic skin response), and the internal carotid artery (for measuring cardiopulmonary functioning), etc. The ear is also at or near the point of exposure to: environmental breathable toxicants of interest (volatile organic compounds, pollution, etc.); noise pollution experienced by the ear; and lighting conditions for the eye. Furthermore, as the ear canal is naturally designed for transmitting acoustical energy, the ear provides a good location for monitoring internal sounds, such as heartbeat, breathing rate, and mouth motion.

Wireless, Bluetooth®-enabled, and/or other personal communication headsets may be configured to incorporate physiological and/or environmental sensors, according to some embodiments of the present invention. As a specific example, Bluetooth® headsets are typically lightweight, unobtrusive devices that have become widely accepted socially. Moreover, Bluetooth® headsets are cost effective, easy to use, and are often worn by users for most of their waking hours while attending or waiting for cell phone calls. Bluetooth® headsets configured according to embodiments of the present invention are advantageous because they provide a function for the user beyond health monitoring, such as personal communication and multimedia applications, thereby encouraging user compliance. Exemplary physiological and environmental sensors that may be incorporated into a Bluetooth® or other type of headsets include, but are not limited to accelerometers, auscultatory sensors, pressure sensors, humidity sensors, color sensors, light intensity sensors, pressure sensors, etc.

Optical coupling into the blood vessels of the ear may vary between individuals. As used herein, the term “coupling” refers to the interaction or communication between excitation light entering a region and the region itself. For example, one form of optical coupling may be the interaction between excitation light generated from within a light-guiding earbud and the blood vessels of the ear. Light guiding earbuds are described in co-pending U.S. Patent Application Publication No. 2010/0217102, which is incorporated herein by reference in its entirety. In one embodiment, this interaction may involve excitation light entering the ear region and scattering from a blood vessel in the ear such that the intensity of scattered light is proportional to blood flow within the blood vessel. Another form of optical coupling may be the interaction between excitation light generated by an optical emitter within an earbud and the light-guiding region of the earbud.

Embodiments of the present invention are not limited to headsets and devices that communicate wirelessly. In some embodiments of the present invention, headsets and devices configured to monitor an individual's physiology and/or environment may be wired to a device that stores and/or processes data. In some embodiments, this information may be stored on the headset itself.

Embodiments of the present invention may apply to the estimation of parameters at another state (other than resting state) by measuring current state parameters and processing this data via a model to generate an estimate of parameters at the desired state. For example, embodiments of the present invention may be applied to estimating vital parameters at the state of peak metabolism during midday. In another example, embodiments of the present invention may be applied to estimating vital parameters at the state of lowered metabolism associated with evening time, for example, just before bedtime. A more general model or equation 160 for estimating vital parameters at a desired state is presented in FIG. 9.

It should also be understood that user input may be used to improve the accuracy of resting state (or other state) parameters. For example, relationships may exist between resting vs. measured parameters and weight, gender, height, habitual information, and the like. A particular example of habitual information may be the time-of-day someone wakes up in the morning. For example, the time of waking up may replace “7 AM” shown in FIG. 2.

Methods for estimating a physiological parameter at a selected state, according to some embodiments of the present invention, may be applied to wearable sensors as well as nonwearable sensors capable of measuring one or more physiological parameters and physical activity in a time-correlated manner, during enough times of the day to build or execute a time-correlated model. For example, whereas multiple examples of wearable devices have been described herein, alternative embodiments may employ wall-mounted sensors, bed-mounted sensors, car-mounted sensors, portable sensors, or other sensor configurations that can measure physiological parameters or physical activity at a “stand-off” distance from a subject. As a specific example, a wall-mounted camera may be configured to measure the heart rate, breathing rate, and physical activity of a subject and to record a time stamp of that subject. Measuring heart rate or breathing rate with a mounted camera may be achieved via algorithms capable of assessing individual video frames for changes in the chest size in time or by detecting certain wavelengths of light associated with heat changes, for example. Additionally, physical activity may be assessed by algorithms capable of identifying subjects and subject motion and translating this identified motion to activity level. In such case, a time-correlated relationship function may be generated for the subject. Thus, the heart rate or respiration rate of the subject may be accurately estimated for a selected state, such as a resting state or other state, when the subject is not in view of the camera by applying the time-correlated relationship function for the subject at the selected state. Suitable stand-off detection methods may employ, for example, electromagnetic, electrical, magnetic, inductive, capacitive, thermal, acoustic, or other energy detection techniques. For example, the heart rate, breathing rate, and activity of a subject sleeping in a bed, and coupled to a stand-off capacitive or inductive sensor, may be monitored through changes in capacitance or inductance. If this data is time-stamped by a processor, the inventive aspects described herein may be applied for determining one or more physiological parameters for that subject at a selected state, such as a state of reduced or elevated activity.

The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although a few exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. The invention is defined by the following claims, with equivalents of the claims to be included therein. 

That which is claimed is:
 1. A method of estimating a value of a physiological parameter for a subject at a selected metabolic state, the method comprising: obtaining, via a device located a distance from the subject, a value of the physiological parameter of the subject at a time-of-day, wherein the device comprises a sensor configured to measure heart rate, breathing rate, and/or physical activity of the subject, wherein the sensor is an electromagnetic energy sensor, an electrical energy sensor, a magnetic energy sensor, an inductive energy sensor, a capacitive energy sensor, a thermal energy sensor, or an acoustic energy sensor; and estimating the value of the physiological parameter for the subject at the selected metabolic state by applying a time-dependent relationship function to the obtained physiological parameter value via at least one processor, wherein the selected metabolic state is different from a current metabolic state of the subject.
 2. The method of claim 1, wherein the time-dependent relationship function is derived from a circadian rhythm for the subject.
 3. The method of claim 1, wherein the time-dependent relationship function is a lookup table.
 4. The method of claim 1, wherein the physiological parameter includes one or more of the following: subject body temperature, subject heart rate, subject heart rate variability, subject blood gas levels, subject metabolic rate, subject respiration rate, subject blood analyte levels, subject blood pressure, and subject pulse pressure.
 5. The method of claim 1, wherein estimating the value of the physiological parameter for the subject at the selected metabolic state comprises obtaining the value of the physiological parameter at the same time-of-day for multiple days and determining an average value for the multiple obtained values, and wherein applying the time-dependent relationship function to the obtained physiological parameter value comprises applying the time-dependent relationship function to the average value.
 6. The method of claim 1, further comprising determining if the subject is in a condition of heightened activity at the time-of-day by determining via the device if at least one obtained physiological parameter value is at a level associated with heightened activity, and wherein the time-dependent relationship function is adjusted for the heightened activity condition of the subject prior to estimating the value of the physiological parameter at the selected metabolic state.
 7. The method of claim 1, wherein prior to obtaining a value of the physiological parameter of the subject at the time-of-day, values of the physiological parameter of the subject are obtained at multiple times during at least one previous day, and a personalized time-dependent relationship function between at least one of value of the physiological parameter and a value of the physiological parameter at the selected metabolic state is generated for the subject using the obtained values from the at least one previous day, and wherein applying the time-dependent relationship function to the obtained physiological parameter value comprises applying the personalized time-dependent relationship function to the obtained physiological parameter value via the at least one processor to estimate the value of the physiological parameter at the selected metabolic state.
 8. The method of claim 1, wherein the device further includes an environmental sensor that detects and/or measures environmental condition information in a vicinity of the subject, and further comprising obtaining, via the device, a value of an environmental parameter in a vicinity of the subject at the time-of-day, and wherein applying the time-dependent relationship function to the obtained physiological parameter value comprises applying the time-dependent relationship function and an environmental-dependent relationship function to the obtained physiological parameter value via the at least one processor to estimate the value of the physiological parameter at the selected metabolic state.
 9. The method of claim 1, further comprising adjusting the time-dependent relationship function for one or more of the following prior to estimating the value of the physiological parameter at the selected metabolic state: calories consumed by the subject and blood oxygen level of the subject.
 10. The method of claim 1, wherein the selected metabolic state includes one or more of the following: state of peak metabolism, state of lowered metabolism, state of rest.
 11. The method of claim 1, wherein the sensor is a wall-mounted sensor, a bed-mounted sensor, a vehicle-mounted sensor, or a portable sensor.
 12. The method of claim 1, wherein the sensor is configured to identify subject motion and to translate identified subject motion to subject activity level.
 13. A system, comprising: a sensor configured to measure heart rate, breathing rate, and/or physical activity of a subject located a distance from the sensor, wherein the sensor is an electromagnetic energy sensor, an electrical energy sensor, a magnetic energy sensor, an inductive energy sensor, a capacitive energy sensor, a thermal energy sensor, or an acoustic energy sensor; and at least one processor configured to obtain from the sensor a value of a physiological parameter of the subject at a time-of-day, and to estimate a value of the physiological parameter for the subject at a selected metabolic state by applying a time-dependent relationship function to the obtained physiological parameter value, wherein the selected metabolic state is different from a current metabolic state of the subject.
 14. The system of claim 13, wherein the at least one processor is configured to: obtain from the sensor the value of the physiological parameter at the same time-of-day for multiple days; determine an average value for the multiple obtained values; and apply the time-dependent relationship function to the average value.
 15. The system of claim 13, wherein the at least one processor is configured to: determine if the subject is in a condition of heightened activity at the selected time-of-day by determining if a heart rate of the subject is at an elevated level; and adjust the time-dependent relationship function for the elevated heart rate level of the subject prior to estimating the value of the physiological parameter at the selected metabolic state.
 16. The system of claim 13, wherein the at least one processor is configured to: obtain values of the physiological parameter of the subject at multiple times during at least one previous day; generate a personalized time-dependent relationship function between a measured value of the physiological value and the estimated value of the physiological parameter at the selected metabolic state using the obtained values from the at least one previous day; and estimate the value of the physiological parameter for the subject at the selected metabolic state by applying the personalized time-dependent relationship function to the obtained physiological parameter value.
 17. The system of claim 13, further comprising an environmental sensor that detects and/or measures environmental condition information in a vicinity of the subject, and wherein the at least one processor is configured to obtain a value of an environmental parameter in a vicinity of the subject at the time-of-day from the environmental sensor, and to apply the time-dependent relationship function and an environmental-dependent relationship function to the obtained physiological parameter value to estimate the value of the physiological parameter at the selected metabolic state.
 18. The system of claim 13, wherein the at least one processor is configured to adjust the time-dependent relationship function for one or more of the following prior to estimating the value of the physiological parameter at the selected metabolic state: calories consumed by the subject and blood oxygen level of the subject.
 19. The system of claim 13, wherein the at least one processor is configured to adjust the time-dependent relationship function for blood oxygen level of the subject prior to estimating the value of the physiological parameter at the selected metabolic state.
 20. The system of claim 13, wherein the sensor is configured to be wall-mounted, bed-mounted, vehicle-mounted, or portable.
 21. The system of claim 13, wherein the sensor is configured to identify subject motion and to translate identified subject motion to subject activity level. 